Medical professionals use images of a patient's eye fundus to screen for and diagnose various diseases, such as diabetic retinopathy. Cameras produce images of the fundus while the patient has been administered pharmacological pupil dilation substances, known as mydriatic fundus imaging, or without pharmacological pupil dilation, known as non-mydriatic fundus imaging. Because pupil dilation is inversely related, in part, to the amount of ambient light, non-mydriatic fundus imaging usually occurs in low lighting environments. Medical professionals can also use fundus imaging apparatus to detect or monitor other diseases, such as hypertension, glaucoma, and papilledema.